In a hard or floppy disc drive system, a read/write head or transducer is moved across a data storage track so as to be positioned over a selected one of the large number of substantially circular, concentric tracks on which data is recorded and/or reproduced. The transducer is mounted on an actuator so as to be positioned in response to control signals transmitted to the actuator. The actuator carriage used in conjunction with this invention typically moves in rotary fashion to move the transducer radially across the disc surface from the innermost track to the outermost track.
In most hard disc drive systems, a plurality of discs are stacked on a spindle, and a corresponding plurality of magnetic heads are used to read and/or write data on each of the surfaces of the discs. The magnetic heads fly over the surface of the discs on an air cushion generated by the rapid rotation of the discs themselves. When power is turned off, the disc slowly spins down to a stop, and the actuator carriage is driven or mechanically biased to move the magnetic heads to an information-free parking or landing zone on which they may rest without destroying information, which is recorded only in other areas of the discs. Typically, the actuator carriage brings the heads quickly to the parking zone in the case of error or a loss of power, and generally a crash stop is provided to prevent further movement of the actuator carriage once it reaches its stop position. The crash stop is conventionally in the form of a pin which may or may not be preloaded.
Given the relatively small sizes of disc drives, for example to read and write on a 2.5 and 1.8-inch disc drive, it is a significant part of the design of the disc drive to precisely position the actuator carriage at the stop position to minimize the area of information-free parking zone. This zone is essentially wasted disc surface space, since no information can be recorded thereon. This parking zone is normally located inside the innermost data recording track on the disc. Another positioning consideration is that a crash stop must be located at the opposite end of the path of travel of the rotary actuator. As the actuator seeks from track to track, it accelerates and decelerates very quickly. It would be extremely damaging to the transducer heads for the transducer to be inadvertently moved off the edge of the surface of the disc.
A further problem with prior art forms of crash stops is that they have relied on a rubber pad or rubber coating to cushion the impact of the actuator arm upon the crash stop. However, rubber causes stiction which can hold the arm after impact, such that the voice coil motor cannot recover the arm's mobility. This is a major problem in miniature disc drives having voice coil motors (VCM's) with reduced torque.
Once the actuator carriage has been moved to its rest position abutting the crash stop, with the transducer now located over the parking zone on the disc surface, it is frequently desirable to latch the actuator carriage or hold it in place, for example, when the disc drive is being moved, so that the heads will not move from the parking zone. This is important because the heads are essentially resting on the surface of the disc in the parking zone, and could be damaged if caused to slide across the surface of the disc. The latch itself has to fit and function within the strict design tolerances of the disc drive system. It is it undesirable to use a solenoid to actively hold the actuator, since this would require a constant current, and therefore a constant drain on a battery or other power source. The design must also take into account the fact that the actuator carriage is heavy relative to the latch, and will therefore exert some force on the latch when the disc drive is tilted or shaken during movement.